1) Field of the Invention
The present invention relates to an organic thin film obtained by forming an organic thin film on a substrate followed by peeling the film therefrom, and a process for producing an organic thin film, which comprises forming an organic thin film on a substrate, followed by peeling the film therefrom, where the peeling can be made easily.
2) Description of the Related Art
One example of organic thin film obtained by forming an organic thin film on a substrate, followed by peeling the film therefrom is a pellicle, which can be used by fixing it to a photo mask or a reticle used in the photolithographic process in the production of semiconductor integrated circuits, and the photo mask or reticle will be hereinafter referred to merely as xe2x80x9cmaskxe2x80x9d.
The pellicle is a dust cover for photomasks or reticles for use in production of large-scale integration circuits and substrates for liquid crystals.
The pellicle is provided above the mask at a specific distance from the mask. Thus, even if fine foreign matters, etc. are attached to the pellicle in the photolithographic process, none of their images is projected on a photoresist-coated semiconductor wafer. That is, by protecting a mask by a pellicle, short circuits, disconnection, etc. of semiconductor integrated circuits can be protected, thereby improving production yields of photolithographic process, and furthermore reducing number of mask cleaning operations, which leads to prolonged mask life. It is the pellicle that can attain such effects.
Light source for irradiation in the photolithographic process includes an ultrahigh pressure mercury lamp, and its g line (xcex=436 nm), h line (xcex=405 nm) and i line (xcex=365 nm) are used as emission lines for the irradiation.
With recent technological progress in the semiconductor industry, integrated circuits of higher density and higher degree of integration are now available and projection patterns with smaller line width and interline distance on a wafer are also now available. Consequently, light sources for irradiation with shorter wavelength are utilized now. For example, far ultraviolet rays (Deep UV) by an excimer laser of krypton fluoride (KrF), argon fluoride (ArF), etc. can be used. To meet the light sources of shorter wavelength, light-stable pellicles transparent to such higher energy radiation beams are now keenly desired.
To meet such requirements, pellicles composed of fluorine-based materials or silicon-based materials have been proposed. The materials include, for example, fluorine-based materials such as tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers (JP-B63-27707), fluorine-based polymers having a perfluoro-alkyl ether ring structure, i.e. CYTOP (trademark of a product commercially available from Asahi Glass Co., Ltd., Japan), Teflon AF (trademark of a product commercially available from E.I. du Pont de Nemours and Co., Inc., USA), etc., and polymeric organosilicone compounds such as polytrimethylvinylsilane, etc. (JP-A-2-230245), etc.
A reflection-preventing single, double or multiple layer can be provided on one side or both sides of a pellicle.
Materials proposed for a reflection-preventing layer(s) as an outermost layer(s) include, for example, tetrafluoroethylene-vinylidene fluoridehexafluoro-propylene polymer (JP-A-61-209449), polyfluoroacrylate (JP-A-1-100549), fluoropolymer having a ring structure on the principal chain, i.e. Teflon AF (trademark of a product commercially available from E.I. du Pont de Nemours and Co., Inc., USA, JP-A-3-39963), CYTOP (trademark of a product commercially available from Asahi Glass Co., Ltd., Japan), etc.
Most of the materials for the outermost reflection-preventing layer are fluorine-containing polymers or inorganic fluorine materials such as calcium fluoride, magnesium fluoride, etc. Most of materials for a transparent thin film layer (central layer) are cellulose derivatives such as nitrocellulose, cellulose acetate propionate, carbonated acetyl cellulose, etc.
Such a pellicle has been so far produced by forming a film from such pellicle materials as mentioned above on a smooth substrate of glass, quartz, Si wafer or the like, followed by peeling it therefrom. A pellicle composed of fluorine-based materials or silicon-based materials, when formed on the substrate, has a high adhesiveness to the substrate, so that the film is hard to peel from the substrate, thereby leading the film to breaking or wrinkling.
When a pellicle film is to be formed on a substrate by forming the outermost reflection-preventing layer and so on successively in this order, the outermost reflection-preventing layer is hard to peel from the substrate, because it is composed of fluorine-based materials and consequently has a high adhesiveness to the substrate.
So far proposed methods for peeling the film from the substrate include, for example, a method for peeling by dipping into water (JP-A-58-219023; JP-A-60-35733; JP-A-2-64, etc.), a method for peeling by dipping in a chemical solution and then in water (JP-A-56-83941), a method for peeling from a substrate in a wet state (JP-A-62-39859), a method for peeling in an atmosphere at a relative humidity of 60% or higher (JP-A-6-67410), a method for peeling upon cooling to 5xc2x0 C. or lower (JP-A-1-166045), etc.
However, peeling by the above-mentioned methods have such problems as deterioration of light transmissivity, uneven film thickness, etc. Particularly, dipping into water or chemical solution has such problems as contamination of pellicle films and deterioration of light transmittance. Peeling in a wet state or in an atmosphere at a relative humidity of 60% or higher has such problems as unevenness of film thickness (color unevenness and difficult process control besides the problem of deteriorated light transmittance due to the fouling of pellicle film. Furthermore, peeling upon cooling to 5xc2x0 C. or lower has such problems as a failure to obtain desired effects, depending on pellicle materials, process complication, etc.
Substrate that has been once peeled off the pellicle film has such a problem as contamination of substrate surface, and thus the film-peeled substrate must be cleaned or repolished before its reuse.
An object of the present invention is to provide a wrinkle-free organic thin film having a high light transmittance and a uniform film thickness and also to provide a process for producing an organic thin film readily peelable from the substrate, the substrate being repeatedly reusable as a recycle substrate, as distinguished over the above-mentioned prior art.
As a result of extensive studies to solve the above-mentioned prior art problems, the present inventors have found that a wrinkle-free organic thin film having a high light transmittance and a uniform film thickness can be obtained by forming an organic thin film on the surface of a substrate having a contact angle of the surface to water of 90xc2x0 or higher, or particularly an organic thin film comprising a fluorine-based material or a silicon-based material on a substrate having a specific silicon compound on the surface, thereby making the formed organic thin film readily peelable from the substrate, and the substrate that has been peeled off the film repeatedly reusable as a recycle substrate, and have established the present invention.
A first aspect of the present invention is to provide an organic thin film obtained by forming an organic thin film on the surface of a substrate having a contact angle of the surface to water of 90xc2x0 or higher, followed by peeling the film therefrom.
A second aspect of the present invention is to provide an organic thin film obtained by forming an organic thin film comprising a fluorine-based material or a silicon-based material on the surface of a substrate having a layer comprising a silicon compound having a perfluoroalkyl group formed on the surface, followed by peeling the film therefrom.
A third aspect of the invention is to provide an organic thin film according to the first or second aspect of the present invention, wherein the organic thin film is in a single layer.
A fourth aspect of the present invention is to provide an organic thin film according to any one of the first to third aspects of the present invention, wherein the organic thin film is a pellicle.
A fifth aspect of the present invention is to provide an organic thin film according to the first, second or fourth aspect of the present invention, wherein the organic thin film is a pellicle comprising a reflection-preventing layer composed of a fluorine-based material and a transparent thin film layer.
A sixth aspect of the present invention is to provide an organic thin film according to any one of the second to fourth aspects of the present invention, wherein the layer comprising a silicon compound having a perfluoroalkyl group is formed by vapor deposition.
A seventh aspect of the present invention is to provide an organic thin film according to any one of the second to fourth aspects of the present invention, wherein the silicon compound having a perfluoroalkyl group is a compound represented by the following formula (1):
CF3(CF2)nCH2CH2Si(OMe)3xe2x80x83xe2x80x83(1)
where n is an integer of 5 to 7 and Me is a methyl group.
An eighth aspect of the present invention is to provide a process for producing an organic thin film, which comprises forming an organic thin film on the surface of a substrate having a contact angle of the surface to water of 90xc2x0 or higher, followed by peeling the film therefrom.
A ninth aspect of the present invention is to provide a process for producing an organic thin film, which comprises forming an organic thin film comprising a fluorine-based material or a silicon-based material on the surface of a substrate having a layer comprising a silicon compound having a perfluoroalkyl group formed on the surface, followed by peeling the film therefrom.
A tenth aspect of the present invention is to provide a process for producing an organic thin film according to the eighth or ninth aspect of the present invention, wherein the organic thin film is in a single layer.
An eleventh aspect of the present invention is to provide a process for producing an organic thin film according to any one of the eighth to tenth aspects of the present invention, wherein the organic thin film is a pellicle.
A twelfth aspect of the present invention is to provide a process for producing an organic thin film according to the eighth, ninth or eleventh aspect of the present invention, wherein the organic thin film is a pellicle comprising a reflection-preventing layer composed of a fluorine-based material and a transparent thin film layer.
A thirteenth aspect of the present invention is to provide a process for producing an organic thin film according to any one of the ninth to eleventh aspects of the present invention, wherein the layer comprising a silicon compound having a perfluoroalkyl group is formed by vapor deposition.
A fourteenth aspect of the present invention is to provide a process for producing an organic thin film according to any one of the ninth to eleventh aspects of the present invention, wherein the silicon compound having a perfluoroalkyl group is a compound represented by the following formula (1):
CF3(CF2)nCH2CH2Si(OMe)3xe2x80x83xe2x80x83(1)
where n is an integer of 5 to 7 and Me is a methyl group.
The present invention provides a wrinkle-free organic thin film having a high light transmittance and a uniform film thickness and a process for producing an organic thin film readily peelable from a substrate, the substrate being repeatedly reusable as a recycle substrate. Particularly by forming a layer comprising a silicon compound having a perfluoroalkyl group on the substrate by vapor deposition an organic thin film having a good surface smoothness, and a very high light transmittance and particularly readily peelable from the substrate can be obtained.
Substrate for use in the formation of the present organic thin film includes those composed of glass such as soda lime, etc., quartz, Si wafer, etc. The substrate must have a sufficiently smooth surface.
The substrate for use in the present invention is a substrate so treated as to give a contact angle of the substrate surface to water of 90xc2x0 or higher or a substrate originally having a contact angle to water of 90xc2x0 or higher.
The contact angle of the substrate surface to water means an angle formed between the substrate surface and a tangential line drawn to the top free side of a water droplet on the substrate surface at the contact point of the substrate surface and the down contact side of the water droplet on the substrate surface, the angle covering the entire periphery of water droplet. The water droplet is of pure water.
Any treating procedure can be used to make the contact angle of the substrate surface to water 90xc2x0 or higher, including, for example, formation of a layer comprising a silicon compound having a perfluoroalkyl group on the surface of a substrate. Such formation of a silicon compound having a perfluoroalkyl group on the substrate can be made by any procedure, but preferably by spin coating or vapor deposition, more preferably by vapor deposition.
Vapor deposition means deposition of vapors of a silicon compound having a perfluoroalkyl group onto a substrate.
Vapor deposition of a silicon compound having a perfluoroalkyl group onto a substrate can be carried out under an atmospheric, subatmospheric or superatmospheric pressure. A silicon compound having a perfluoroalkyl group and a substrate are placed into a container, where the substrate is formed with vapors of the silicon compound having a perfluoroalkyl group preferably under an atmospheric or subatmospheric pressure at a forming temperature of preferably 5 to 200xc2x0 C., more preferably 20xc2x0 to 130xc2x0 C. The container is preferably tightly sealed, but may have a ventilation port to the outside. Forming time is preferably one minute to one week, more preferably one hour to 3 days.
Substrate having a layer comprising a silicon compound having a perfluoroalkyl group formed on the surface is used as a substrate for forming an organic thin film thereon.
Silicon compound having a perfluoroalkyl group includes, those represented by the following formulae (2), (3), (4) and (5):
CF3(CF2)7CH2CH2Si(OMe)3xe2x80x83xe2x80x83(2)
CF3(CF2)5CH2CH2Si(Ome)3xe2x80x83xe2x80x83(3)
CF3(CF2)7CH2CH2SiMe(OMe)2xe2x80x83xe2x80x83(4)
CF3(CF2)5CH2CH2SiMe(OMe)2xe2x80x83xe2x80x83(5)
where Me is a methyl group; silazanes having a perfluoroalkyl group; and their oligomers, etc.
Among these compounds, the compound represented by the foregoing formula (2) (i.e. 10,10,10,9,9,8,8,7,7,6,6,5,5,4,4,3,3-heptadecafluoro-decyltrimethoxysilane) is particularly preferable.
An organic thin film is formed on the substrate having a layer of silicon compound having a perfluoro-alkyl group formed thereon by vapor deposition.
Thickness of the organic thin film so formed is 50 xcexcm or less, preferably 10 xcexcm or less.
The present organic thin film can be formed by any procedure, but spin coating is preferable because of distinguished precision of film thickness and surface characteristics. Spin coating depends on many factors such as solution viscosity; solvent evaporation rate, spin coater surrounding temperature and humidity, spin revolutions per minute, spin time, etc., and thus the factors must be properly selected.
Materials for the organic thin film are the above-mentioned fluorine-based materials and silicon-based materials such a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer, CYTOP, Teflon AF, polytrimethylvinylsilane, polytriethylvinylsilane, polyethyldimethylvinylsilane, etc. These materials can be used alone or in mixture of at least two thereof.
When the organic thin film is in the form of pellicle, these materials can be irradiated with light, for example, radiations such as xcex3-rays, electron beams, xcex1-rays, etc., or far ultraviolet rays or the like to improve the solution filtrability, electric controllability, adhesiveness to pellicle support frame, etc.
Solvent for the fluorine-based materials includes, for example, perfluoroalkane, perfluorobenzene, perfluoro (2-butyltetrahydrofuran), trichlorotrifluoro-ethane, perfluorotripropylamine, perfluorotributylamine, etc. and mixtures thereof.
Solvent for the silicon-based materials includes, for example, benzene, toluene, xylene, etc. Boiling point of these solvents is preferably 70xc2x0 C. or higher, more preferably 100xc2x0 C. or higher.
Solution of the materials for the organic thin film must be subjected to spin coating after filtration to remove foreign matters, etc. The thickness of the resulting organic thin film can be properly selected by changing the solution viscosity and revolutions per minute of the substrate. The solvent contained in the organic thin film formed on the substrate can be evaporated off by a hot plate, an oven etc.
The organic thin film formed on the substrate is then bonded to a double faced tape-pasted support frame of metal, plastic, etc. at room temperature in air. Then, the organic thin film can be obtained by peeling the support frame from the substrate. Since the substrate has a contact angle of the surface to water of 90xc2x0 or higher obtained by vapor deposition of the silicon compound having a perfluoroalkyl group on the surface of the substrate, the wrinkle-free organic thin film having a high light transmittance and a uniform thickness can be peeled from the substrate.
Furthermore, the substrate that has been peeled off the organic thin film can be repeatedly reused as a recycle substrate directly without cleaning for further formation of organic thin films, followed by peeling.
When the organic thin film is in the form of a pellicle, the pellicle can be bonded to the support frame, by an ultraviolet curing type adhesive, a thermosetting type adhesive or the like or by melt bonding or by a thick polymer solution as an adhesive.
In case of a pellicle having a single reflection-preventing layer on both sides, a reflection-preventing layer is at first formed on the substrate and, after thorough solvent evaporation from the reflection-preventing layer by drying, a transparent thin film layer (central layer) is then formed on the reflection-preventing layer. After thorough solvent evaporation from the transparent thin film layer by drying, another reflection-preventing layer is formed thereon. The triple layer film thus formed on the substrate is bonded to a double faced tape-pasted support frame of metal, plastic, etc. By peeling the support frame from the substrate, a pellicle triple layer film can be easily obtained thereby, because the silicon compound having a perfluoroalkyl group has been vapor deposited on the substrate surface in advance.
A pellicle having a double reflection-preventing layer on both sides can be likewise obtained by successively forming a low refractive index, reflection-preventing layer, a high refractive index, reflection-preventing layer, a transparent thin film layer (central layer), a high refractive index, reflection-preventing layer and a low refractive index, reflection-preventing layer on a substrate, bonding a support frame thereto, followed by peeling from the substrate. The five-layered film as bonded to the support frame can be easily obtained.
Materials for the transparent thin film layer (central layer) include, for example, cellulose derivatives such as nitrocellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, ethyl cellulose, carbonated acetyl cellulose, etc. The cellulose derivatives can be used alone, but nitro-cellulose has a distinguished film strength and a form retainability at a high humidity but has a poor light stability, as compared with other cellulose derivatives. Cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate have a distinguished light stability, but have a poor film strength and a poor form retainability at a high humidity. Thus, it is preferable to use a mixture of nitrocellulose and at least one of other cellulose derivatives.
A mixing proportion of nitrocellulose to at least one of other nitrocellulose depends on the desired film strength, form retainability at a high humidity and light stability, but the nitrocellulose content of the mixture is preferably 10 to 50% by weight, more preferably 20 to 40% by weight. It is preferable to use cellulose derivatives having a higher molecular weight, because of a better form retainability of the thin film. That is, the molecular weight is 30,000 or more, preferably 50,000 or more in terms of number average molecular weight. Among the cellulose derivatives, nitrocellulose is commercially available from Asahi Chemical Industry Co., Ltd., Japan, and cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate are commercially available from Eastman-Kodak Co., USA.
Solvent for the cellulose derivatives includes, for example, 2-butanone, methyl isobutyl ketone, cyclohexanone, butyl acetate, isobutyl acetate, ethyl lactate, cellosolve acetate, propyleneglycol monomethyl ether acetate, etc. and a mixture thereof. Solutions of cellulose derivatives are subjected to spin coating after filtration to remove foreign matters therefrom. Thickness of the transparent thin film (central layer) can be properly selected by changing the solution viscosity and revolutions per minute of the substrate. The solvent contained in the thin film formed on the substrate can be evaporated off by a hot plate, an oven, etc.
The reflection-preventing layer is in a single or double or multiple layer structure. In case of a single layer reflection prevention [the number of layers in a pellicle will be 3 (triple layer) when the reflection-preventing layer is formed on both sides of the transparent thin film layer], the reflection-preventing effect will be a maximum when the relation between the refractive index n1 of the reflection-preventing layer and the refractive index nc of the transparent thin film (central layer) is n1=(nc)1/2, and a larger reflection-preventing effect can be obtained by selecting reflection-preventing materials having a refractive index n1 nearer to (nc)1/2. Let the reflection-to-prevent wavelength be xcex, thickness d of the reflection-preventing layer must be selected to satisfy a relation of n1xc2x7d=xcex/4.
In case of a double layer reflection prevention (the number of layers in a pellicle will be 5 when the double reflection-preventing layer is formed on both sides of the transparent thin film layer as in the same manner as above), the layer in contact with the transparent thin film layer will be a high refractive index, reflection-preventing layer and the outermost layer will be a low refractive index, reflection-preventing layer. Let the refractive indices and thicknesses of the outermost reflection-preventing layer and the reflection-preventing layer in contact with the transparent thin film layer be n1 and d1, and n2 and d2, respectively, the reflection-preventing effect will be a maximum, when n2/n1=(nc)1/2, and a larger reflection-preventing effect can be obtained by selecting reflection-preventing layer materials having n2/n1 nearer to (nc)1/2. Let the reflection-to-prevent wavelength be xcex, thicknesses d1 and d2 of the reflection-preventing layers must be selected to satisfy a relation of n1xc2x7d1=n2xc2x7d2=xcex/4. For the central layer, cellulose derivatives, polyvinylbutyral, polyvinylpropional, etc. can be used, where their refractive indice nc are about 1.5, and thus (nc)1/2 will be about 1.22. That is, in case of the double layer reflection prevention, a larger reflection-preventing effect can be obtained preferably, when materials for the double reflection-preventing layer are selected to have a ratio of their refractive indice n2/n1 nearer to 1.22.
Materials for the low refractive index, reflection-preventing layer for use as the outermost layer include, for example, fluorine-based materials such as tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene polymer, polyfluoroacrylate, Teflon AF (trademark of fluorine-based polymer having a cyclic structure on the principal chain, commercially available from E.I. du Pont de Nemours and Co., USA), CYTOP (trademark of a product commercially available from Asahi Glass Co., Ltd., Japan), etc. Preferable polyfluoroacrylate is FC-722 (trademark of a product commercially available from Sumitomo 3M Co., Ltd., Japan). In case of Teflon AF, [filterability] filterability, electric controllability and adhesiveness between the pellicle film and the support frame can be improved by irradiation of light such as radiations, e.g. xcex3-rays, electron beams, xcex1-rays, etc., or far ultraviolet rays or like.
The fluorine-based materials for the reflection-preventing layer can be used alone or in mixture of other polymers. The fluorine-based polymer is dissolved into a fluorine-based solvent such as perfluorobenzene, perfluoro (2-butyltetrahydrofuran), trichlorotrifluoroethane, perfluorotributylamine, etc., but to obtain a smooth film surface free from color unevenness a high boiling point solvent is preferable. The boiling point is preferably 130xc2x0 C. or higher, more preferably 160xc2x0 C. or higher.
The fluorine-based polymer solution is subjected to spin coating after filtration to remove foreign matters therefrom in advance. Thickness of low refractive index, reflection-preventing layer for use as the outermost layer can be properly selected by changing the solution viscosity and revolutions per minute of the substrate. The solvent contained in the thin film formed on the substrate can be evaporated off by air drying or by a hot plate, an oven, etc.
In case of the double layer reflection-preventing pellicle, materials for the high refractive index, reflection-preventing layer in contact with the transparent thin film layer include, for example, polyvinylnaphthalene, polystyrene, polyether sulfone, etc. The pellicle with the reflection-preventing layers can be bonded to a support frame by an adhesive such as an ultraviolet-curing type adhesive or a thermosetting type adhesive. It is preferable to use an ultraviolet-curing type adhesive because of process simplicity and less damage to the pellicle film.
The present invention will be described in detail below, referring to Examples and Comparative